Is it a business decision (ie dont want to canabalize the prime market) or a technical limitation (physically can't do it with current tech) or cost issue (technical difficulties would require that the lens be priced too high for target market)?

They certainly can (thanks for the link above, but mfd of 8 ft ) but I don't think anyone would like to carry one around. A zoom, at least for me, is about convenience, so while an ultra fast zoom would be great, it would cost a small fortune and be a b*tch to carry around. All you have to do is troll this forum and you'll constantly see folks opting for the f4 versions of many a zoom simply because the 2.8 is already heavy so an even faster zoom would presumably be even heavier.

I think a 35 to 85 f1.8 could be done in a size smaller than a 200 f2L and probably a lower weightpossibly even as small as an 82mm filter I think by limiting the wide end to 35 you are not running into all the wide angle problems super zooms encounter

Possible, but I don't see your reason for wanting them as it massively adds to cost (the glass they have to put in) and it just gets heavier and heavier, even though they're sharp as heck now and 2.8 is really good for zooming. I was surprised to find my 24-70 II A LOT heavier than my 70-200 f/4 IS. As you know, it'd be a better option to go for a prime to get apertures larger than f/2.8 due to the lighter construction

But then again, I'd probably be VERY tempted into buying a 70-200 f/1.8L IS

Hobby Shooter

I posted a similar question a few weeks ago, I couldn't find that thread now but will have a look again to see if I can get it for you. As I understand it, a 70-200 f/1.8 for example would be just too big to carry and too expensive to buy basically.